This invention relates to relief valves. More specifically, this invention relates to relief valve assemblies for controlling charge flow pressure in a hydrostatic pump.
A typical direct acting relief valve has a high pressure rise rate. As the flow increases through the relief valve the pressure at the inlet increases. The typical pressure rise rate is greater than two bars per ten 1 μm of flow. This increase of pressure is a power drain from the engine.
The pressure rise rate associated with relief valves is dependent on the back pressure in the cavity or exit port. The spring chamber of the valve is referenced to the back pressure in the cavity. In a typical screw-in valve cavity the pressure within the cavity at the exit is variable as a function of the radial location relative to the spring chamber vent location. The pressure is lowest near the cavity exit and it is highest at 180 degrees from the exit. The typical method to sense the downstream pressure is with an opening such as a drilled hole or a slot that connects to the spring chamber of the valve. Because the valve is a screw-in type, the radial orientation of the spring chamber vent within the cavity cannot be controlled. The pressure rise rate is dependent upon the radial location of the spring chamber vent relative to cavity exit.
Therefore, it is a principal object of the present invention to significantly reduce the radial orientation effect on the pressure rise rate in a relief valve within a hydrostatic pump.
Yet another object of the present invention is to provide an improved relief valve to control the charge flow pressure in a hydrostatic pump that minimizes rise rate.
These and other advantages, features, or the like will become apparent from the specification and the claims.